Continuous Application of Polyglycerol‐Supported Salen in a Membrane Reactor: Asymmetric Epoxidation of 6‐Cyano‐2,2‐dimethylchromene

Abstract

In the current work, suitability of hyperbranched polyglycerol as a high loading catalyst support is demonstrated. A polyglycerol-supported manganese-salen complex (chemzyme) is applied as a homogeneous catalyst in the epoxidation of 6-cyano-2,2-dimethylchromene. The recyclability of the corresponding catalyst was investigated in repetitive batch experiments as well as a continuous operation of the reaction in an ultrafiltration membrane reactor. An enhanced stability of the catalyst in repetitive batches was observed as a result of immobilization whereby the total turnover number increased from 23 in a single batch to 80 in four repetitive batches. To enable continuous operation, a continuously operated, stirred tanked reactor (CSTR) was equipped with an ultrafiltration membrane (MPF-50) and a retention of 98% was determined. The continuous chemzyme membrane reactor was operated over the course of 20 residence times. After approximately 12 residence times, the steady state was reached yielding 70% conversion as well as an enantiomeric excess up to 92%. A space-time yield (sty) of 458 g L À1 d À1 and a turnover frequency (TOF reaction ) of up to 18 h À1 was reached in the steady state. It was determined that the total turnover number (TTN) was enhanced by a factor of 10 from 24 (batch) up to 240 for 20 residence times in CSTR operation.

Continuous Flow System Using Polymer‐Supported Chiral Catalysts

“…In this case, one aromatic ring has a hydroxymethyl functionality instead of a second t-butyl group in the 4 position. catalyst 14, the support is a soluble, star-shaped hyperbranched polymer derived from glycerol, whereas an MPF-50 membrane is used for the retention of the catalyst in the first compartment [52]. The system has been applied to the enantioselective epoxidation of a chromene using m-CPBA/NMO as the oxidizing reagent.…”

Recyclable Stereoselective Catalysts

“…Epoxidation of 6 -cyano -2,2 -dimethylchromene, using catalyst 63 ( Fig. 1.29 ), was carried out in a continuously operated chemical membrane reactor for 20 residence times, and steady conversions up to 70% as well as steady ee ' s of up to 92% were achieved (total TON = 240) [127] .…”

Polyurethane‐ and Polystyrene‐Supported 2,2,6,6‐Tetramethyl‐ piperidine‐1‐oxyl (TEMPO); Facile Preparation, Catalytic Oxidation and Application in a Membrane Reactor

“…[38,39] Moreover, membrane technology offers the possibility of performing the process in a continuous manner. [40,41] In the current work, application of homogeneous PU-TEMPO catalyst 3 in a continuously operated chemical membrane reactor is investigated as well.…”